[Autofill/Autocomplete Feature] Substring matching instead of prefix matching.

components/autofill/content/renderer/password_autofill_agent.cc

Index: components/autofill/content/renderer/password_autofill_agent.cc
diff --git a/components/autofill/content/renderer/password_autofill_agent.cc b/components/autofill/content/renderer/password_autofill_agent.cc
index 237f23a2055d901e576ffbec07b6c432635b31fc..f6084b9ecc481e783a53da533efb7bd8a6ad36f2 100644
--- a/components/autofill/content/renderer/password_autofill_agent.cc
+++ b/components/autofill/content/renderer/password_autofill_agent.cc
@@ -17,6 +17,7 @@
 #include "components/autofill/content/renderer/renderer_save_password_progress_logger.h"
 #include "components/autofill/core/common/autofill_constants.h"
 #include "components/autofill/core/common/autofill_switches.h"
+#include "components/autofill/core/common/autofill_util.h"
 #include "components/autofill/core/common/form_field_data.h"
 #include "components/autofill/core/common/password_form.h"
 #include "components/autofill/core/common/password_form_fill_data.h"
@@ -225,7 +226,8 @@ bool DoUsernamesMatch(const base::string16& username1,
                       bool exact_match) {
   if (exact_match)
     return username1 == username2;
-  return StartsWith(username1, username2, true);
+  return StartsWith(username1, username2, true) ||
+         IsContentsPrefixOfSuggestionToken(username1, username2, true);
 }
 
 // Returns |true| if the given element is editable. Otherwise, returns |false|.
@@ -415,8 +417,16 @@ bool FillUserNameAndPassword(
     username_element->setAutofilled(true);
 
     if (set_selection) {
-      username_element->setSelectionRange(current_username.length(),
-                                          username.length());
+      if (IsFeatureSubstringMatchEnabled()) {
+        size_t start =
+            autofill::GetTextSelectionStart(username, current_username);
+        if (start != base::string16::npos) {
+          username_element->setSelectionRange(start, username.length());
+        }
+      } else {
+        username_element->setSelectionRange(current_username.length(),
+                                            username.length());
+      }
     }
   } else if (current_username != username) {
     // If the username can't be filled and it doesn't match a saved password
@@ -753,13 +763,24 @@ bool PasswordAutofillAgent::PreviewSuggestion(
     return false;
   }
 
+  base::string16 current_username = username_element.value();
+  base::string16 suggested_username = username;
   was_username_autofilled_ = username_element.isAutofilled();
   username_selection_start_ = username_element.selectionStart();
   username_element.setSuggestedValue(username);
   username_element.setAutofilled(true);
-  username_element.setSelectionRange(
-      username_selection_start_,
-      username_element.suggestedValue().length());
+
+  if (IsFeatureSubstringMatchEnabled()) {
+    size_t start =
+        autofill::GetTextSelectionStart(suggested_username, current_username);
+    if (start != base::string16::npos) {
+      username_element.setSelectionRange(start, suggested_username.length());
+      was_username_autofilled_ = start;
+    }
+  } else {
+    username_element.setSelectionRange(
+        username_selection_start_, username_element.suggestedValue().length());
+  }
 
   was_password_autofilled_ = password_info->password_field.isAutofilled();
   password_info->password_field.setSuggestedValue(password);